Hundreds of so-called "hoodie marches" have been taking place on an ad-hoc basis as community leaders, students and celebrities protest against the police reaction.

'Hoodie' marches have sprung up across the United States since Tuesday. Credit: www.democraticunderground.com

17-year-old Trayvon Martin was an shot dead in Sanford, Floriday on February 26th by 28-year-old George Zimmerman.

Martin had been watching an NBA basketball game on TV a his father's girlfriend's house in a gated community when he left the house to walk to a nearby 7-Eleven.

On his way back from the shop he was spotted by George Zimmerman.

On the 21st March thousands of protesters marched in solidarity with the family of Trayvon Martin. Credit: Reuters

Zimmerman called the police to report "suspicious behaviour" in his area, he told police he was following the young man. The police told him this was not necessary, however he continued to do so.

When they turned up, Trayvon was dead, and Zimmerman was not arrested as he claimed he acted in self-defence.

Florida has a "stand your ground law" that allows someone in fear of "great bodily harm" to respond with deadly force. This controversial law is now being reviewed by a specially appointed state task force.

Students Trayvon Martin's Sanford High School made a human chain of his initials today. Credit: ITV News

The family of Trayvon have been campaigning for his killer to be arrested for murder and have launched an online petition which has so far been signed by more than 1.5 million people.

As details of the 911 call emerged, a host of celebrities on twitter urged people to march, sign the petition and to join what has become an national movement for justice.